Aspects of cellular aging will be studied in a system based on the culture of amphibian eggs in vitro. Eggs from Xenopus laevis when aged in culture develop both chromosomal abnormalities and developmental abnormalities. These two abnormalities are reminiscent of abnormalities seen when human eggs age in utero. Thus, inferences drawn from these proposed studies may elucidate general biological mechanisms involved in causing chromosomal abnormalities of human eggs such as trisomy 21 (Down's syndrome). Amphibian egg aging is particularly well suited for experimental study because these cells show effects of aging when maintained in culture for less than a day. Thus the eggs' rapid development of chromosomal abnormalities will allow many experiments to be performed relatively quickly once the basic parameters of the culture system are established. The amphibian system will be particulary useful because cytoplasmic and nuclear transfers will show 1) where the causative agent is localized within the cell and 2) whether a factor(s) can be transferred that accelerates (or retards) the rate of appearance of chromosomal abnormalities. This study will 1) develop a system well suited for studying the cause of chromosomal abnormalities, 2) determine whether intrinsic cellular factors are localized and transferable, and 3) lead to purification of the causative agent. This study also will expand conceptual and experimental approaches relating expression of egg aging in vitro to aging of related human cells in vivo.